The invention relates to an optical detection device including a photodetector element and outputting an electrical signal according to a light amount received by the photodetector element, an optical device including such an optical detection device on a substrate, an optical device including an irradiating means irradiating a target object with a light, and an optical information reading device including such optical devices and reading information indicated by a code symbol in which modules having different light reflectivity from surroundings are arranged. Further, the invention also relates to a light source fixing method for fixing a light source unit to the above-described optical device.
A code symbol called a bar code or a two-dimensional code is an image formed of modules of black bars (or simply “bars”) with low light reflectivity and white bars (or spaces) with high light reflectivity.
In general, a method is well known which represents information related to an item by such a code symbol, prints or attaches this code symbol to the item, and reads this code symbol with an optical information reading device. As a field of use, a POS (Point Of Sales) system disposed in a retail store such as a supermarket or the like is a representative example, but besides that, the field ranges broadly over distribution of goods, mail service, event place management, medical service, chemical inspection, and so on.
Then, to classify roughly, as the optical information reading device, there are laser code scanners using laser and area sensor scanners using a camera which uses a CCD (Charge Coupled Device), CMOS (Complementary Metal Oxide Semiconductor), or the like. Among them, as compared to the area sensor scanners, the laser code scanners have a long history and technologies built up, and hence are highly reliable.
In such a laser code scanner, there is mounted a small light scanning module which scans a reading target object with a light flux (laser light) using a semiconductor laser element as a light source, and decodes information from a reflected light thereof. Then, for this light scanning module, a method to rotate a polygon mirror and a scanning mirror method to vibrate one mirror are known as methods for deflecting a laser light for scanning.
For example, PTL1 describes a bar code reader which emits a light from a light emitting element such as a semiconductor laser and reflects the light by one surface of the polygon mirror toward the reading target object. PTL2 describes an optical information reading device in which a laser beam emitted from a light emitting unit is reflected by a vibrating mirror, which vibrates in a seesaw manner, toward the reading target object.
In these devices, for illuminating the reading target object with a large amount of light fluxes, the former device is equipped with a polygon mirror having many reflecting surfaces, and the latter device vibrates a mirror with one surface. The amount of light fluxes illuminating the reading target object relates also to accuracy when decoding the code symbol, and illuminating with a large amount of light fluxes enables good decoding.